Containers for beverages such as milk, fruit juices, and drinks are conventionally constructed from blanks of thermoplastic coated paperboard. The most widely used of such containers have a rectangular cross-sectional body surmounted by a gable-top closure incorporating an extensible pouring spout. Blanks from which the containers are constructed are divided into a plurality of panels which are adapted to form the walls and closure members. The panels are formed and separated by score lines at which the blank is folded. Particular panels are intended to be joined together in a lapped arrangement in the completed container. Typically, those panels are pressed together and heated or exposed to high frequency radiation to fuse the adjoining thermoplastic surfaces and form a generally strong seal. To finally seal the filled container, two or more panels are finally joined and sealed to form a rib along the top edge of the roof panels. Exemplary of such container blanks are those shown in Alden U.S. Pat. No. 2,750,095 and Wilcox U.S. Pat. No. 3,245,603.
Containers of this type are opened for access to the contents by a two-step toggle action process. First, the gable edges of the roof panels at the front of the container are pushed outward and upward toward the rear of the container by thumb pressure, breaking the seal between the outside surfaces of the two lip panels, and breaking the seal in the rib panels surmounting the roof above the pouring spout. The gable edges are forced backward past the point at which the lip panels are joined, to nearly touch the roof panels.
Second, the gable edges are pushed forward and towards each other. The forces are communicated through spout panels to the tip of the pouring spout, breaking the seal between the lip panels and the underside of the roof panels and snapping the spout outward to a pouring position.
Typically, the highest level of resistance is encountered during the initial breaking of the seal of the pouring spout panels at the onset of the first phase of the opening process described hereinabove. The remainder of the first phase involves a continued opening at an elevated level of force, although reduced somewhat from the initial opening force. The second phase, that of extending the panels of the pouring spout forward to enable dispensing of the contents of the gable-top container, exhibits a further reduced level of opening force, compared to the previous levels.
In early models of gable-top containers, the panels comprising the lips of the pouring spout were bonded to the underside of the roof panels. The resulting sealed spout was difficult to open, generally requiring insertion of a tool behind the lips to separate them from the roof underside. The cardstock panels often tore or delaminated in an uncontrolled manner, producing an unsightly and unsanitary container. In those cases where an adhesive was applied to only those panels which were to be joined, it was simple to eliminate adhesive from the spout panels to reduce the forces required to open the spout. The resulting container, of course, was not effectively sealed and was subject to leakage.
An improvement in gable-top containers to provide a hermetic seal for an extended shelf life package consisted of coating the inner surface of the container blank with a metallic foil and an overcovering layer of thermoplastic such as polyethylene. The panels to be sealed are bonded by heating the thermoplastic surface coatings to a softening or melting temperature, compressing the panels together and cooling. The use of thermoplastic coatings or foil adds some stiffness to the panels, and the container is made resistant to wicking by liquids. However, the strong bonding of the lip panels results in uncontrolled and irregular buckling, tearing and delamination of the cardstock upon opening the seal. Thus, the spout is difficult to open, and the opened panels are unappealing in appearance.
As used in the food packaging industry, the term hermetic refers to a container designed and intended to be secure against the entry of oxygen which degrades flavor. The term is also used to designate containers used for aseptic filling and storage, i.e. containers secure against the entry of microorganisms. The hermetic barrier of such cartons typically comprises an aluminum or other barrier film coating the inner surface, overcovered with a thermoplastic such as polyethylene. The carton wall thickness is thus increased, resulting in larger channels where the edges of overlying panels have a stepped relationship in the gable rib area, increasing the chance for leakage.
Attempts to provide an easily opened spout seal have included (a) perforations in the spout panels which tear open to expose pouring lips, (b) improved control of the sealing temperature, (c) the use of added scoreline patterns to concentrate the opening forces, and (d) the use of anti-adhesion agents, i.e. abhesives, to reduce the required opening forces.
The use of perforations in the spout panels has generally been unsatisfactory. Such perforations produce a spout of reduced size, which requires special sealing operations. The perforations are considered by some to be a weak point in the carton, prone to develop leaks. This type of carton spout requires external forces such as thumbnail pressure to open, and this procedure is considered unsanitary. The carton cannot be effectively closed, once opened, and shaking of the carton results in spillage.
Likewise, efforts to reduce temperature variations in the sealing process have not produced a satisfactory hermetic sealing gable-top container. Because of narrow acceptable temperature range for obtaining the desired adhesion, sealing variations persist in spite of improved temperature control. Moreover, the required opening forces generally exceed the panel strength, even where minimal sealing is achieved.
The use of novel scoreline patterns generally has not overcome the strong sealing forces of well-sealed spouts and buckling of the spout panels is common.
One method for preventing the difficulty in opening the completely bonded lip panels of polyethylene coated gable-top containers is shown in Crawford et al, U.S. Pat. No. 3,116,002. In this reference, a thin coating of a high molecular weight organo-siloxane gum is applied to the lip panels as an abhesive, that is, to prevent permanent adhesion to the panels in contact with the lip panels.
Egleston et al, U.S. Pat. No. 3,270,940 discloses the use of an anti-adhesive composition applied to both the outside and inside surfaces of the pouring lip of a gable-top container. Abhesive agents disclosed include cellulose plastic laminated to polyethylene, the latter heat-bondable to the polyethylene surface of the cardstock blank.
The release properties of abhesives are generally affected by the heat sealing parameters and are inconsistent. Containers designed for hermetic use and having adhesives in the spout sealing area often require opening forces greater than the wall strength of the panels, and the spout panels buckle during the opening process.
The problems of conventional gable-top containers in this respect is aggravated by containers such as are disclosed in U.S. Pat. No. 4,787,507, the contents of which are incorporated herein by reference. The gable-top container of the '507 patent is representative of gable-top constructions that incorporate new and/or additional layers that enhance the properties of the container in regard to flavor retention, prevention of oxygen penetration, or other like features that increase the shelf life, integrity and freshness of the contents of the container. However effective these new and/or additional layers may be for their intended purpose, they also inherently introduce additional toughness and tear resistance to the gable-top container thus formed and at the same time increase the force required to open the gable-top container thus constructed, particularly during the first phase of the opening process described above, after the initial separation of the pouring spout panels.
Thus, it is desirable to provide a gable-top container having a reduced opening force. This problem is not adequately solved by any of the conventional gable-top container designs, and in particular with gable-top containers constructed from higher strength laminates.